Fluorous tagging compounds and methods of use thereof

ABSTRACT

A method of increasing the fluorous nature of a compound includes the step of reacting the compound with at least one second compound having the formula:                    
     wherein Rf is a fluorous group and m is 0, 1 or 2.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is divisional patent application of U.S. patentapplication Ser. No. 09/583,247, filed May 31, 2000, the disclosure ofwhich is incorporated herein by reference.

GOVERNMENTAL INTERESTS

This invention was made with government support under grant CA 78039awarded by the National Institutes of Health. The government has certainrights in this invention.

FIELD OF THE INVENTION

The present invention relates to fluorous tagging or protectingcompounds and to methods of use thereof, and especially, to fluoroustagging compounds suitable for use with hydyroxy- and amine-bearingorganic compounds.

BACKGROUND OF THE INVENTION

In traditional organic chemistry, compounds are synthesized as puresubstances through well-planned reactions and careful separation.However, in a number of fields, including drug discovery, catalystdesign and new material development, tens of thousands of organiccompounds must be synthesized and tested to discover a few active ones.In the pharmaceutical industry, for example, synthesizing such a largenumber of compounds in the traditional way is too slow compared to therapid emergence of new biological targets. The productivity of orthodoxsolution (liquid) phase organic synthesis is severely limited by tediousseparation processes for the purification of products. Techniquesintegrating organic reactions with rapid purification/separationprocedures are thus highly desirable.

Recently, fluorous synthetic and separation techniques have attractedthe interest of organic chemists. In fluorous synthetic techniques,reaction components are typically attached to fluorous groups or tagssuch as perfluoroalkyl groups to facilitate the separation of products.Organic compounds are readily rendered fluorous by attachment of anappropriately fluorinated phase label or tag. In general,fluorous-tagged molecules partition preferentially into a fluorous phasewhile non-tagged ones partition into an organic phase.

The fluorous tag preferably fulfills a double role as protective groupand phase tag and is removed in the final step(s) of the synthesis. Theviability of a fluorous synthesis plan depends greatly on theavailability of suitable fluorous protecting groups, but only a fewfluorous tags are currently available.

In that regard, the fluorous phase label or tag most often used influorous synthesis has been the silane (C₁₀F₂₁CH₂CH₂)₃SiBr 1. Ingeneral, the silane is attached to alcohol-bearing substrates usingstandard conditions to result in a silyl ether, and can be cleaved withfluoride. The silane, however, cannot be recycled. In addition, thepowerful electron withdrawing effect of three fluorous chains makes thesilyl ether rather labile towards nucleophiles and other polarreactions. Thus, although fluorous synthetic and/or separationtechniques are promising, such techniques are currently limited by alack of availability of suitably versatile fluorous tags.

It is thus very desirable to develop improved fluorous taggingcompounds.

SUMMARY OF THE INVENTION

For the further development of fluorous phase chemistry into a practicalstrategy in, for example, combinatorial and parallel synthesis, avariety of fluorous phase labels must be made available. The presentinvention provides fluorous tags that can be prepared in large quantity,can be installed and removed from a substrate using mild reactionconditions, and can be recyclable after cleavage. In addition, thefluorous tags of the present invention are tolerant, as a group, to awide range of reaction conditions, such that an appropriate label can bechosen which is amenable to substantially any given sequence ofreactions.

The resulting fluorous “tagged” compound can be used in a wide varietyof fluorous reaction and/or separation techniques. Several fluorousreaction and separation techniques are disclosed, for example, in U.S.Pat. Nos. 5,859,247 and 5,777,121, the disclosures of which areincorporated herein by reference. The tagging compounds of the presentinvention are particularly suitable for tagging of compounds bearinghydroxyl groups or nitrogen groups such as amine groups.

As used herein, the term “fluorous”, when used in connection with anorganic (carbon-containing) molecule, moiety or group, refers generallyto an organic molecule, moiety or group having a domain or a portionthereof rich in carbon-fluorine bonds (for example, fluorocarbons orperfluorocarbons, fluorohydrocarbons, fluorinated ethers, fluorinatedamines and fluorinated adamantyl groups). For example, perfluorinatedether groups can have the general formula —[(CF₂)_(x)O(CF₂)_(y)]_(z)CF₃,wherein x, y and z are integers. Perfluorinated amine groups can, forexample, have the general formula —[(CF₂)_(x)(NR^(a))CF₂)_(y)]_(z)CF₃,wherein R^(a) can, for example, be (CF₂)_(n)CF₃, wherein n is aninteger. Fluorous ether groups and fluorous amine groups suitable foruse in the present invention need not be perfluorinated, however. Theterm “fluorous compound,” thus refers generally to a compound comprisinga portion rich in carbon-fluorine bonds. As used herein, the term“perfluorocarbons” refers generally to organic compounds in which allhydrogen atoms bonded to carbon atoms have been replaced by fluorineatoms. The terms “fluorohydrocarbons” and “hydrofluorocarbons” includeorganic compounds in which at least one hydrogen atom bonded to a carbonatom has been replaced by a fluorine atom. A few examples of suitablefluorous groups Rf for use in the present invention include, but are notlimited to, —C₄F₉, —C₆F₁₃, —C₈F₁₇, —C₁₀F₂₁, —C(CF₃)₂C₃F₇, —C₄F₈CF(CF₃)₂, —CF₂CF₂OCF₂CF₂OCF₃, —CF₂CF₂ (NCF₂CF₃) CF₂CF₂CF₃, and fluorousadamantyl groups.

As used herein, the term “tagging” refers generally to attaching afluorous moiety or group (referred to as a “fluorous tagging moiety” or“tagging group”) to a compound to create a “fluorous tagged compound”.Separation of the tagged compounds of the present invention is achievedby using fluorous separation techniques that are based upon differencesbetween/among the fluorous nature of a mixture of compounds. As usedherein, the term “fluorous separation technique” refers generally to amethod that is used to separate mixtures containing fluorous moleculesor organic molecules bearing fluorous domains or tags from each otherand/or from non-fluorous compounds based predominantly on differences inthe fluorous nature of molecules (for example, size and/or structure ofa fluorous molecule or domain or the absence thereof). Fluorousseparation techniques include but are not limited chromatography oversolid fluorous phases such as fluorocarbon bonded phases or fluorinatedpolymers. See, for example, Danielson, N. D. et al., “Fluoropolymers andFluorocarbon Bonded Phases as Column Packings for LiquidChromatography,” J. Chromat., 544, 187-199 (1991). Examples of suitablefluorocarbon bonded phases include commercial Fluofix® and Fluophase™columns available from Keystone Scientific, Inc. (Bellefonte, Pa.), andFluoroSep™-Octyl from ES Industries (Berlin, N.J.). Other fluorousseparation techniques include liquid-liquid based separation methodssuch as liquid-liquid extraction or countercurrent distribution with afluorous solvent and an organic solvent.

Preferably, the molecular weight of the fluorous tags of the presentinvention does not exceed about 2,500. More preferably, the molecularweight does not exceed about 1,750. Even more preferably the molecularweight does not exceed about 1200. Compounds may bear more than onefluorous tag of the present invention.

In one aspect, the present invention provides a method of increasing thefluorous nature of a compound, including the step of reacting thecompound with at least one second compound having the formula:

wherein Rf is a fluorous group and m is 0, 1 or 2 (that is, the ring canbe a five-, six-, or seven-membered ring). The fluorous group can, forexample be a fluorohydrocarbon group (for example, fluorous alkylgroups, including fluorous adamantyl groups), a perfluorocarbon group, afluorinated ether group or a fluorinated amine group. Perfluoroadamantylgroup suitable for use in the present invention can, for example, havethe following formulas:

As used herein, the terms “alkyl”, “aryl” and other substituent groupsrefer generally to both unsubstituted and substituted groups unlessspecified to the contrary. Unless otherwise specified, alkyl groups arehydrocarbon groups and are preferably C₁-C₁₅ (that is, having 1 to 15carbon atoms) alkyl groups, and more preferably C₁-C₁₀ alkyl groups, andcan be branched or unbranched, acyclic or cyclic. The term “aryl” refersto phenyl (Ph) or napthyl, substituted or unsubstituted. The term“alkylene” refers to bivalent forms of alkyl.

The groups set forth above, can be substituted with a wide variety ofsubstituents. For example, alkyl groups may preferably be substitutedwith a group or groups including, but not limited to aryl groups. Arylgroups may preferably be substituted with a group or groups including,but not limited to, alkyl groups or other aryl groups.

In another aspect, the present invention provides a method of increasingthe fluorous nature of a compound, including the step of reacting thecompound with at least one second compound having the formula:

wherein Rf is a fluorous group as defined above, R¹ is a an alkyl groupor an aryl group and m is 0, 1 or 2.

A method of increasing the fluorous nature of a compound, including thestep of reacting the compound with at least one second compound havingthe formula:

wherein Rf¹ and Rf² are independently, the same or different, fluorousgroups, Rs¹ is a spacer group, d is 1 or 0 (that is, the spacer groupcan be present or absent), Rs² is a spacer group, a is 1 or 0, R² is aH, an alkyl group or an aryl group, R³ is H or —Rs³ _(e)Rf³, wherein,Rs³ is a spacer group, e is 1 or 0, and Rf³ is a fluorous group.Numerous types of spacer groups or linkages can be used in the presentinvention. Examples of spacer groups suitable for use herein include,but are not limited to, alkylene groups (preferably, C₁-C₆ alkylenegroups), 1,2-, 1,3-, or 1,4-divalent phenyl groups or alkoxy alkylenegroups (for example, —O(CH₂)_(x)—). As used herein, the term “alkylene”refers generally to a bivalent form of an alkyl group (for example,—(CH₂)_(m)—) Alkylene groups may be substituted or unsubstituted.

The present invention also provides a method of increasing the fluorousnature of a compound, including the step of reacting the compound withat least one second compound having the formula:

wherein Rf¹ and Rf² are independently, the same or different, fluorousgroups, Rs¹ is a spacer group, d is 1 or 0 (that is, the spacer groupcan be present or absent), Rs² is a spacer group, a is 1 or 0, R⁴ is analkyl group or an aryl group, R⁵ is an alkyl group or an aryl group, R⁶is H, an alkyl group, or a fluorinated alkyl group, and X is Cl, Br orI.

In another aspect, the present invention provides a method of increasingthe fluorous nature of a compound, including the step of reacting thecompound with at least one second compound having the formula:

wherein Rf¹ is a fluorous group, Rs¹ is a spacer group, d is 1 or 0, R⁴is an alkyl group or an aryl group, R⁵ is an alkyl group or an arylgroup, and X is Cl, Br or I.

The present invention further provides a compound having the formula:

The present invention also provides a compound having the formula:

The present invention also provides a compound having the formula:

The present invention also provides a compound having the formula:

The present invention further provides a compound having the formula:

In another aspect, the present invention provides a method of activatingan anomeric sulfoxide to react with an alcohol to form a correspondingether comprising the step of mixing the anomeric sulfoxide withCp₂ZrCl₂, AgClO₄, and the alcohol. The anomeric sulfoxide can, forexample, have the formula:

In still another aspect, the present invention provides a method ofcarrying out a reaction comprising the steps of:

attaching a fluorous tag to a substrate that is bound to a solidsupport;

cleaving the fluorous-tagged substrate from the solid support whileretaining the fluorous tag attached thereto;

reacting the cleaved, fluorous-tagged substrate in a liquid phasereaction to synthesize a fluorous-tagged product; and

separating the fluorous-tagged product from other compounds using afluorous separation technique.

The method may further include the step of cleaving the fluorous tagfrom the fluorous tagged product. In one embodiment, the fluorous taghas the formula:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrate synthesis of one embodiment of a fluorous glycosyliodide tagging compound of the present invention and fluorous-taggedethers synthesized therefrom.

FIG. 2 illustrate synthesis of one embodiment of a fluorous sulfoxidetagging compound of the present invention and fluorous-tagged etherssynthesized therefrom.

FIG. 3 illustrates synthesis of one embodiment of a fluorous vinyl ethertagging compound of the present invention and fluorous tagged ethersproduced therefrom.

FIG. 4 illustrates synthesis of one embodiment of a fluorous alkoxysilyltagging compound of the present invention and fluorous tagged ethersproduced therefrom.

FIG. 5 illustrates the tagging of a number of alcohols with the fluorousalkoxysilyl tag of FIG. 4 and subsequent regeneration of the alcohol andrecycling of the fluorous alkoxysilyl tag.

FIGS. 6 and 7 illustrate synthesis of combinatorial mixtures using thefluorous tag of FIG. 3.

FIG. 8 illustrates characterization of several products of the synthesisof FIGS. 6 and 7 (peaks 1-6 correspond to compounds 43-48,respectively).

FIG. 9 illustrates an example of conversion from a solid phase synthesisto a liquid phase synthesis using the fluorous tag of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Fluorous-Labeled Tetrahydropyranyl (THP^(F)) Ethers

In one aspect the present invention provides a series offluorous-labeled tetrahydropyranyl (THP^(F)) ethers that are stable tobasic and nucleophilic reaction conditions and become readily recyclableafter cleavage. A perfluoroalkyl-substituted dihydropyran which can beinstalled on any hydroxy-bearing substrate via acid catalysis in thesame way a standard THP protection is provided as a model.

Initially, dihydropyran 4 was synthesized in one step fromperfluorooctyl iodide 3 and dihydropyran 2 in 46% yield as illustrate inFIG. 1. However, treatment of alcohols with an excess of 4 using avariety of acids, solvents, and temperatures failed to give any of thedesired acetal 5. The loss of reactivity of the vinyl ether is believedto be a result of the powerful electron withdrawing effect of theperfluoroalkyl chain.

A second route involved glycosylation methodology. Glycosyl fluorideshave been effectively activated by a Cp₂ZrCl₂—AgClO₄ reagent system.Suzuki, K. Pure Appl. Chem. 1994, 66, 1557. Flourous glycosyl iodide 6was accessible in one step from perfluorooctyl iodide 3 with excessdihydropyran and stoichiometric Na₂S₂O₄/NaHCO₃ under phase transferconditions in 64% yield. Unfortunately, this reaction was oftenirreproducible, and was typically plagued by formation of hemiacetal 7.Use of catalytic Raney Nickel in refluxing THF gave 6 more reliabilityin 32-38% yield. Addition of a slight excess of 6 to a solution of oneequivalent of Cp₂ZrCl₂, two equivalents of AgClO₄, and one equivalent ofan alcohol gave good yields of fluorous THP labeled products 8,presumably via an intermediate highly reactive oxonium species.Deprotection via transacetalization with methanol and catalyticpara-toluenesulfonic acid proceeded to give the free alcohol in 80-95%yield, as well as the transacetalization product 9. However, attempts torecylcle methyl THP ether 9 to iodopyran 6 have yet to be successful.Application of trimethylsilyl iodide (TMSI) and several of its in situprepared variants led in all cases to the undesired elimination product4 as the primary product.

A sulfoxide method, however, has proven to be a mild and effective meansfor constructing glycosidic linkages. See Yan, L.; Kahne, D. J. Am.Chem. Soc. 1996, 118, 9239, and references cited therein. The synthesisof fluorous tetrahydropyranyl (THP^(F)) ethers of the present inventionusing this technique, began with the direct synthesis of methyl THPether 9 from perfluorooctyl iodide 3 and dihydropyran 2. Treatment of amethanolic solution of 3 and 5 mol % [CpFe(CO)₂]₂ (cyclopentadienyl irondicarbonyl dimer) with 1.5 equiv of dihydropyran and 1.1 equiv of Et₃Nat room temperature gave 9 in 83% yield. Conversion of 9 to thephenylthioacetal 10 was first accomplished using Nicolaou's method (5equiv PhSSiMe₃ (phenylthiotrimethylsilane), 1.2 equiv Me₃SiOTf(trimethylsilyltrifluoromethanesulfonate)) to give 10 in 60% yield.Nicolaou, K. C.; Seitz, S. P.; Papahatjis, D. P. J. Am. Chem. Soc. 1983,105, 2430. Alternatively, heating 9 in a 1:1 mixture of PhSH(thiophenol) and toluene at 100° C. with 1 equiv of para-toluenesulfonicacid gave 10 in 61% yield. Oxidation of sulfide 10 with aNa₂HPO₄-buffered solution of meta-chloroperoxybenzoic acid indichloromethane at 0° C. provided fluorous sulfoxide tagging compound 11as a 1.5:1 mixture of anomers in 72% yield. Subsequent conversionutilized the major, more reactive cis-isomer. Trans-11 could be recycledto a 1:1 mixture of anomers in thiophenol/dioxane (1:1) at 95° C. in thepresence of a catalytic amount of HgSO₄.

Attempted glycosylation of alcohols with 11 using the standard triflicanhydride/2,6-di-tert-butyl-4-methyl pyridine reagent system gave lowyields of 8 contaminated with large amounts of a dihydropyranelimination product 4. In contrast, treatment of a 1:2:1 mixture ofCp₂ZrCl₂, AgClO₄, and alcohol at −20° C. with 1.5-2.5 equivalents of 11provided after 8-10 h the desired fluorous THP labeled ethers 12-20illustrated in FIG. 2 (ROTHP^(F)) in good yields for 1° and 2° alcohols.In addition, deprotection of the THP^(F)-ethers and recycling of theprotective group was accomplished by a transacetalization reaction using25 mol % para-toluenesulfonic acid in MeOH:THF (2:1) at 70° C. for 20-30h to give good yields of recovered alcohols and 9.

Purification of most THP^(F)-ethers was accomplished simply bydissolving the crude product in MeCN and extracting five times withFC-72. FC-72 is a fluorocarbon solvent commercially available (3M) whichincludes perfluorohexane (C₆F₁₄) isomers (bp 56° C.). Concentration ofthe fluorous extracts yielded the fluorous product, which containedsmall amounts of a dihydropyran elimination product 4, as well as traceamounts of unreacted sulfoxide 11. After this extraction, only minoramounts of the fluorous product remained in the MeCN layer. The crudedeprotection mixture, treated with the same MeCN/FC-72 extractionprocedure, gave the fluorous methyl-THP ether 8 in the FC-72 extracts,while the deprotected alcohol was found in the organic layer. As theorganic mass or the polarity of a fluorous THP-labeled substrate becomeslarger, however, simple liquid-liquid extraction becomes inefficient.Solid phase extraction by filtration through fluorous reverse-phase(FRP) silica gel was found to be effective for these cases. See Curran,D. P.; Hadida, S.; He, M. J. Org. Chem. 1997, 62, 6714. The rather polar5 is almost insoluble in FC-72. This is advantageous in terms ofseparation of excess 11 during extractive purification ofTHP^(F)-labeled alcohols, but also suggests a sufficiently polar moietyon the substrate to be protected may overpower the fluorous nature ofthe protected product. Fluorous THP-labeled cholesterol and methylmandelate could not be fully extracted from MeCN with multiple (15)FC-72 extractions. Loading of the crude product onto a MeCN-wettedFRP-SiO₂ column, washing first with MeCN to elute organic components,then with FC-72 to elute the fluorous labeled compounds, convenientlyallowed separation of THP^(F)-labeled ethers from organic side products.

The recyclable fluorous THP tag or protecting group enables simplepurification of small molecules by liquid-liquid extraction withFC-72/MeCN, and of larger or more polar molecules by solid phaseextraction with fluorous reverse phase silica gel.

Fluorous Vinyl Ether Tags

In another aspect, the present invention provides a recyclable fluorousvinyl ether tagging or protecting group that is attached and removedunder mildly acidic conditions.

A representative example of the synthesis of a fluorous vinyl ethertagging compound is illustrated in FIG. 3. The synthesis of vinyl ether23 begins with commercially available iodide 21. Formation of theGrignard reagent from 21 was effectively accomplished with sonicationfor the reaction initiation. Thus, treatment of an ether suspension ofexcess magnesium powder with 0.1 equivalents of 21, sonication for 20minutes, and subsequent addition of an additional 2.4 equivalents of 21in Et₂O provided the Grignard reagent after a two hour reflux period.Dropwise addition of one equivalent of ethyl formate to the reactionmixture and further refluxing for 5 h gave the crude fluorous alcohol 22after standard workup. This compound was conveniently purified bywashing the crude solid with dichloromethane to give a 93% yield of 22.Vinylation (See Faulkner, D. J.; Petersen, M. R. J. Am. Chem. Soc. 1973,95, 553) of 22 with 0.5 equivalents of mercuric acetate in a 1:1 mixtureof ethyl vinyl ether and FC-72 at 45° C. for 40 h gave fluorous vinylether tagging compound 23 in 51% yield, with 42% recovered alcohol 22(88% yield based on recovered starting material). The extremely apolar23 could be isolated by filtration of the crude product mixture througha short pad of SiO₂ with hexanes, since the RF value of 23 is 0.9 inhexane, while 22 has an R_(F) close to zero in hexane. The R_(f) valueof a compound is a measure of the relative polarity of the compound in agiven solvent system. Thus, a compound with R_(f)=1 is very nonpolarrelative to a compound with R_(f)=0, which would be considered verypolar. The unreacted 22 can then be resubjected to the vinylationreaction, allowing for a ˜70% conversion to 23 after two runs.Accordingly, vinyl ether 23 is readily prepared in multigram quantities.

Protection of alcohols with 23 proceeds under mildly acidic conditions.Treatment of an Et₂O solution of 1 equivalent of a primary alcohol and 3equivalents of 23 with 5 mol % of camphorsulfonic acid for 3 h at roomtemperature provided the desired protected alcohols 24 (ROAE^(F)) in84-93% yields, with the majority of the excess of vinyl etherrecoverable. Secondary and even tertiary alcohols are similarlyprotected in good yields using THF as solvent at 65° C. for 30-45 min.The moderate yield obtained for protection of tert-butyl alcoholcompares nonetheless well to the protection of this sterically hinderedand volatile substrate with the fluorous THP^(F) lable discussed above.The alkoxy ethyl (AE^(F)) fluorous label could also be installed on thenitrogen atom of an aniline. All protected and fluorous-taggedsubstrates were purified from excess 23 by column chromatography onSiO₂. Separation was generally very straightforward as a result of theconsiderable RF-differences between 23 and 24, and the pre-purificationof the reaction mixture from organic impurities by extraction withFC-72.

Deprotection of fluorous acetals 25-31 proceeded under mild conditionsas well. Treatment of the protected substrates in a 1:1 solution of Et₂Oand MeOH with 5 mol % of camphorsulfonic acid gave, after 1 h, excellentyields of deprotected substrates as well as a quantitative recovery offluorous alcohol 22 (see FIG. 3). After completion of the reaction, theproducts were isolated in pure form by simple 3-phase extraction(reaction mixture/saturated aqueous NaHCO₃/FC-72). Alcohol 22 can beresubjected to vinylation to give 23 and thus is efficiently recycled.

The recyclable, highly fluorous acetal protecting group have broadapplications in fluorous synthesis as well as in fluorous/solid phasecombinations and other parallel synthesis strategies. The precursorvinyl ether 23 can be prepared in large quantities in a straightforwardtwo step reaction sequence. Primary, secondary, and tertiary alcoholscan be protected in good to excellent yields. The N-protection of2-fluoroaniline also demonstrates the feasibility of using 23 withamines. After protection with the AE^(F)-groups of the presentinvention, a compound is capable of undergoing a series of reactions inwhich purification of products can, for example, be accomplished bysimple liquid-liquid extraction with FC-72 or filtration throughfluorous reverse-phase SiO₂. Deprotection occurs under mild acidicconditions, and the fluorous label is easily isolated and effectivelyrecycled.

Compared to the THP^(F)-function described above, the AE^(F)-groups ofthe present invention are more readily cleaved and recycled and have ahigher affinity toward the fluorous environment. There is a directcorrelation between the number of fluorine atoms in a molecule and itsselective solubility in perfluorinated solvents. With the exception ofsmall organic molecules, most compounds protected with theTHP^(F)-function were insufficiently fluorous for efficientliquid-liquid extraction and rapid purification required fluorousreverse-phase SiO₂ (FRP). In particular in preparative scale synthesis,the broad use of FRP chromatography is currently limited by the highcosts of the stationary phase. Because of the higher level offluorination of the AE^(F)-group, all substrates shown in FIG. 3 couldbe purified by simple liquid-liquid extraction. The AE^(F)-group tags orlabels are, therefore, ideally suited for the protection of largequantities or high molecular weight organic molecules under basic and/ornucleophilic reaction sequences. Application of the AE^(F)-fluoroustagging compounds of the present invention to a combinatorial synthesisof analogs of the antimitotic natural product curacin A is discussedbelow.

tert-Butyl-phenyl-1H,1H,2H,2H-heptadecafluorodecyloxysilyl (BPFOS) Tags

In still another aspect, the present invention provides fluorousalkoxysilyl tagging groups. In general,tert-Butyl-phenyl-1H,1H,2H,2H-heptadecafluorodecyloxysilyl (BPFOS)ethers resulting from reaction of the fluorous alkoxysilyl tagginggroups of the present invention with alcohols were found to besurprisingly acid stable and allow simpleprotection-purification-deprotection schemes by liquid-liquid extractionwith FC-72/CH₃CN or by solid phase extraction with fluorous reversephase silica gel.

Given the acid stability of bis-alkoxysilyl ethers, the viability offluorous alkoxysilyl groups as fluorous tagging/protecting groups foralcohols was explored. A secondary alcohol, cyclohexanol, was chosen asa model compound for tagging. As illustrated in FIG. 4, fluorousalkoxysilyl ethers (34a,b) were readily prepared by reactingstoichiometric amounts of commercially available dichlorosilanes 32 withfluorous alcohol 22 to yield chlorosilanes 33a,b, which were howevercontaminated with the bis-adduct of the fluorous alcohol. Withoutpurification, 33a,b were used to protect cyclohexanol as illustrated inFIG. 4. The ensuing mixture was purified by solid phase extraction onfluorous reverse phase silica gel with hexane/acetone (50:1). Theindicated yields were isolated yields after separation from bis-adductsof the fluorous alcohol. Conversion based on cyclohexanol wasquantitative.

Alkoxysilyl ether 37a was derived from bromosilane 36, which can easilybe obtained in high yield and purity in a two step sequence startingfrom tert-butyldiphenylsilylchloride (TBDPS-Cl) and alcohol 35 asillustrated in FIG. 4.

Fluorous alkoxysilyl ethers (34a,b, 37a) were each dissolved in amixture of CH₂Cl₂/trifluoroacetic acid (5%), and aliquots of thesesolutions were quenched with MeOH/pyridine (20:1). The quenched reactionmixtures were analyzed for remaining 34a,b and 37a by LC-MS (Liquidchromatography-mass spectrometry). Reactions and quenching wereperformed on a HP 7868 solution phase synthesizer. Analysis of quenchedsamples was done with a HP 1100 series LC/MS. Samples eluted werecompared with unreacted control samples. (R_(t) [min]: 2.6 (34a), 2.9(34b), 2.3 (37a); Novapak C₁₈, 3.9×150 mm, 1.2 mL/min, MeOH as eluent).

The stability of these alkoxysilyl ethers appeared to be determined bythe steric bulk around the silicon atom. While 34a was not very stable(t_(1/2)˜6 min) under the acidic reaction conditions, 34b (t_(1/2)˜4 h)was moderately stable, and thetert-butyl-phenyl-1H,1H,2H,2H-heptadecafluorodecyloxysilyl ether 37a(t_(1/2)>>6 h) was very stable. These results prompted investigation ofthe chemical behavior of 37a in somewhat greater detail. As a result ofthe enhanced electrophilicity of the silicon atom in bis-alkoxysilylethers, the latter are generally more labile toward nucleophiles andbases than either the TBDPS or the tert-butyldimethylsilyl (TBDMS)groups. Yet, after dissolving 37a in a mixture of THF-d₈ and 0.25 M NaOD(3:1), a t_(1/2) of 48 h was determined by ¹H NMR, suggesting that thetert-butyl-phenyl-1H,1H,2H,2H-hepta-decafluorodecyloxysilyl (BPFOS) tagcan be used in mildly basic aqueous media. In contrast, the stabilityunder protic acidic conditions in 5% p-TsOH/MeOH (t_(1/2)˜40 min) ismore limited. Based on these results, it appears that the BPFOS group isclosely related in stability to the tert-butylmethoxyphenylsilyl group,which is slightly more acid-labile than the TBDPS function butconsiderably more acid-stable than a TBDMS-ether.

The viability of thetert-butyl-phenyl-1H,1H,2H,2H-heptadecafluorodecyloxysilyl (BPFOS)protecting group for the protection of alcohols in a parallel synthesisexperiment performed on a HP 7868 solution phase synthesizer was alsostudied. Silylbromide 36 was reacted with a panel of alcohols to yieldthe bis-alkoxysilyl ethers 37a-f as illustrated in FIG. 5. In general,alcohols 38a-f (0.16 mmol) were added to a solution containing theappropriate amount of reagents in 0.7 mL of CH₂Cl₂. The samples werevortexed and left for 16 h. The solutions were washed with H₂O, theorganic phase was evaporated and the residue was eluted with hexanethrough cartridges containing SiO₂.

Table 1 summarizes data for the protection of alcohols 38a-f with 36 asset forth in the following equation (and deprotection of silyl etherswith TBAF (tetrabutylammonium fluoride)). [ ] Yields were based onisolated and characterized material (¹H NMR, MS) and were slightly lowerthan reported for the bulk synthesis of 37a as a result of loss ofmaterial in the liquid-liquid extraction steps on the synthesizer.Purification in the deprotection step was via FC-72/CH₃CN liquid-liquidextraction and filtration through silica gel, and provided materialof >90% purity. During the deprotection step, silyl ethers 37a-f wereadded to a solution of TBAF (0.6 M) in 0.5 mL of THF. After 3 hours,Et₂O was added, the solutions were washed with H₂O (3 times), the Et₂Ophase was collected, evaporated and the residue was partitioned betweenFC-72 and CH₃CN. The organic phase was eluted with hexane/AcOEt througha SiO₂ cartridge.

TABLE 1 Yield for BPFOS attachment Yield for BPFOS Entry R—OH [%]cleavage [%] 1

79 77 2

77 88 3

24 nd 4

83 94 5

27 nd 6

62 100 

Primary and secondary alcohols gave excellent to fair yields in theprotection and deprotection steps while, probably for steric reasons,the tertiary alcohol t-butanol (entry 5) and the sterically demandingmethyl mandelate (entry 3) provide less favorable yields.

In summary, new acid stable fluorous silane tag suitable for theprotection of primary and secondary alcohols have been developed. Thetag is easily attached and removed in an automated parallel synthesissetup and allows for purification of intermediates and products viafluorous liquid-liquid or solid phase extraction.

Exemplary Applications

Two model applications serve to illustrate the potential use of thenewly developed fluorous tags of the present invention. For example,FIG. 6 illustrates the preparation of aldehyde 39 which is subjected toan in situ obtained mixture of six organolithium reagents. The excess ofreagents converts the aldehyde rapidly to adduct 40, which is trapped byaddition of AE^(F)vinyl ether tag 23 as illustrated in FIG. 7. Only thedesired secondary alcohol products are rendered fluorous with thisapproach and converted to acetals 41, which are readily purified byfluorous techniques, or, if required, by chromatography. The stabilityof the AE^(F) protective group allowed easy manipulation of theseproducts even in an aqueous basic environment, conditions that wouldlead to immediate decomposition of the earlier silyl ether based tags.After separation from the byproducts and reagents, compounds 41 arede-tagged, and the desired mixture of alcohols 42 is obtained in highyield ready for biological testing. The very high level of combinatorialmixture purification that can be obtained with this approach isdemonstrated by the LC-MS trace shown in FIG. 8.

FIG. 9 illustrates a powerful application for the use of BPFOS taggingcompound 36, and demonstrates the first example of a solidphase—fluorous phase switch. Addition of Grignard reagent to thebead-linked aldehyde derived from 49 provides alcohol 50 which istagged/protected as BPFOS-ether 51 and thus rendered both solid andfluorous. After acidic (TFA) cleavage of the solid support, the BPFOStagging group allows the extraction of product 52 into the fluorousenvironment, and subsequent solution phase chemistry can immediatelytake advantage of fluorous phase purification techniques. No existingfluorous silyl ether tag has the stability necessary to allow thisconversion.

Experimental Examples

Compounds 12-20, were obtained in pure form and fully characterized.Cis-11: Mp 66-69° C.; IR (KBr) 3063, 2919, 2853, 1664, 1603, 1445, 1199cm⁻¹; ¹H NMR (CDCl₃)δ 8.00-7.90 (m, 2H), 7.70-7.55 (m, 3H), 4.87 (d, 1H,J=4.3 Hz), 4.50 (dt, 1H, J=11.5, 3.4 Hz), 3.72-3.66 (m, 1H), 3.17-3.00(m, 1H), 2.64-2.56 (m, 1H), 2.05-1.75 (m, 4H); ¹³C NMR (CDCl₃)δ 136.5,134.3, 129.3, 128.9, 125.0-105.0 (m, 8 C), 85.6, 63.3, 32.4 (t, 1 C,J=20.1 Hz), 19.9, 17.5; MS (CI) m/z (rel. intensity) 629 ([M+H]⁺).

General Procedure for Glycosylation. A mixture of 200 mg of powderedmolecular sieves (4 Å), zirconocene dichloride (139 mg, 0.48 mmol),silver perchlorate (200 mg, 0.96 mmol), and 5 mL of CH₂Cl₂ was stirredat room temperature for 10 min. Benzyl alcohol (49.0 μL, 0.47 mmol) wasadded to the yellow solution, and the temperature was lowered to −20° C.A solution of cis-11 (446 mg, 0.71 mmol) in 10 mL of CH₂Cl₂ was added,and the reaction mixture was allowed to warm gradually to roomtemperature. After 10 h, the solution was filtered through a pad ofSiO₂. After rinsing with CH₂Cl₂, the filtrate was concentrated and theresidue partitioned between 4 mL of MeCN and 15 mL of FC-72. The MeCNlayer was washed with 4 additional 10-15 mL portions of FC-72. ¹H NMR ofthe combined fluorous extracts showed the desired product 14 as well aselimination product 4 in a 5.3:1 ratio. ¹H NMR of the MeCN layer showedprimarily excess sulfoxide 11. Chromatography of the FC-72 extract onSiO₂ (hexanes/Et₂O, 97:3) provided pure 14 (264 mg, 0.43 mmol, 92%) as acolorless solid (7.4:1 ratio of diastereomers): Mp 36-37° C.; IR (KBr)3037, 2966, 2879, 1501, 1450, 1358, 1209, 1147 cm⁻¹; Major diastereomer:¹H NMR δ (CDCl₃) 7.37-7.29 (m, 5H), 4.99 (d, 1H, J=3.5 Hz), 4.80 (d, 1H,J=11.6 Hz), 4.54 (d, 1H, J=11.7 Hz), 3.97-3.90 (m, 1H), 3.63 (dt, 1H,J=11.3, 5.0 Hz), 2.60-2.40 (m, 1H), 2.20-2.09 (m, 1H), 1.90-1.80 (m,2H), 1.60-1.50 (m, 1H); ¹³C NMR δ (CDCl₃) 137.4, 128.5, 128.0,125.0-105.0 (m, 8 C), 95.2, 69.6, 61.0, 41.3 (t, 1 C, J=19.5 Hz), 21.9,18.7, 17.4; HRMS (EI) calculated for C₂₀H₁₅O₂F₁₇ 610.0801, found610.0803.

General Procedure for Deprotection of ROTHP^(F)-tagged compounds. Asolution of 14 (112 mg, 0.18 mmol) and p-toluenesulfonic acid (9 mg,0.05 mmol) in 2 mL of MeOH and 2 mL of THF was heated at 70° C. for 24h. The reaction mixture was diluted with Et₂O and washed with asaturated NaHCO₃ solution. The organic layer was dried (Na₂SO₄),concentrated, and partitioned between 2 mL of MeCN and 8 mL of FC-72.The MeCN layer was washed with three 8 mL portions of FC-72. ¹H NMRanalysis of the combined FC-72 extracts showed 9 (82 mg, 0.15 mmol, 84%)with a trace amount of 4. ¹H NMR analysis of the MeCN layer showed purebenzyl alcohol (19.0 mg, 0.176 mmol, 96%).

Preparation of 22: A suspension of 4.2 g (0.173 mmol) of Mg powder and2.5 g (4.36 mmol) of iodide 21 in 20 mL of Et₂O was sonicated for 20min. To this black mixture was added dropwise a solution of 22.5 g (39.2mmol) of iodide 21 in 150 mL of Et₂O. The reaction mixture was heated atreflux for 2 h, and the solution was cannulated away from the excess Mginto a new flask. After dropwise addition of 1.40 mL (17.4 mmol) ofethyl formate, the black solution was heated at reflux for 5 h. Thereaction mixture was cooled to 0° C., quenched with saturated ammoniumchloride solution and extracted with Et₂O. The organic extracts weredried (Na₂SO₄) and concentrated. The crude product was washed withCH₂Cl₂ and dried in vacuo to give 14.92 g (16.15 mmol, 93%) of 22 as awhite solid: Mp 98-101° C.; IR (KBr) 3461, 1204, 1146 cm⁻¹; ¹H NMR(CDCl₃)δ 4.20 (d, 1H, J=6.0 Hz), 3.80-3.73 (m, 1H), 2.60-2.15 (m, 4H),1.95-1.65 (m, 4H); ¹³ C NMR (TFA)δ 125.0-105.0 (m, 16 C), 79.4, 28.4,25.9; MS (EI) m/z (rel. intensity) 907 ([M-OH]⁺, 2), 887 (6), 477 (100).

Preparation of 23: A mixture of 14.92 g (16.15 mmol) of 22, 2.6 g (8.1mmol) of Hg(OAc)₂, 100 mL of ethyl vinyl ether, and 100 mL of FC-72(commercially available from 3M) was heated at reflux for 40 h. Aftercooling to room temperature, the reaction mixture was transferred to aseparatory funnel, and the layers were separated. The organic layer wasextracted with FC-72 (3×), and the combined FC-72 extracts were dried(Na₂SO₄), and concentrated. The crude product was loaded onto a short(1.5″) pad of SiO₂ and washed with hexanes until no more 23 was shown tobe eluting via TLC. The hexane washings were concentrated to give 7.85 g(8.2 mmol, 51%) of 23 as a white solid, Mp 36-38° C. Flushing the SiO₂pad with EtOAc, followed by concentration of the filtrate gave 6.29 g(6.8 mmol, 42%) of 22. Spectroscopic data for 23: IR (KBr) 3131, 1646,1617, 1209, 1151 cm⁻¹; ¹H NMR (CDCl₃)δ 6.27 (q, 1H, J=6.6 Hz), 4.35 (d,1H, J=14.2 Hz), 4.10 (d, 1H, J=6.5 Hz), 3.91 (p, 1H, J=5.5 Hz),2.35-2.00 (m, 4H), 1.95-1.75 (m, 4H); ¹³C NMR (CDCl₃)δ 150.0,125.0-105.0 (m, 16 C), 89.8, 76.4, 26.7 (t, J=22.1 Hz), 24.8; MS (EI)m/z (rel. intensity) 950 (M⁺, 7), 887 (20), 391 (100).

Protection of cinnamyl alcohol: To a solution of 10.5 mg (0.08 mmol) ofcinnamyl alcohol and 223 mg (0.24 mmol) of 23 in 3 mL of Et₂O was added1 mg (5 mol %) of 10-camphersulfonic acid (CSA). The solution wasstirred at room temperature for 3 h. Saturated NaHCO₃ solution wasadded, and the reaction mixture was extracted with FC-72 (3×). Thecombined FC-72 extracts were dried (Na₂SO₄), and concentrated. Columnchromatography on SiO₂ (hexanes/Et₂O, 95:5) gave 101 mg (0.11 mmol, 64%)of 23 and 79 mg (0.073 mmol, 93%) of the desired AE^(F)-protectedcinnamyl alcohol as a colorless oil: IR (neat) 3032, 2981, 1491, 1204,1148, 907 cm⁻¹; ¹H NMR (CDCl₃)δ 7.38-7.21 (m, 5H), 6.60 (d, 1H, J=15.9Hz), 6.25 (dt, 1H, J=5.9, 15.9 Hz), 4.81 (q, 1H, J=5.3 Hz), 4.26-4.13(m, 2H), 3.80 (p, 1H, J=5.5 Hz), 2.40-2.00 (m, 4H), 1.90-1.75 (m, 4H),1.37 (d, 3H, J=5.2 Hz); ¹³C NMR (CDCl₃)δ 136.6, 132.4, 128.7, 127.9,126.5, 125.4, 125.0-105.0 (m, 16 C), 99.0, 73.4, 65.8, 26.4, 20.4; MS(EI) m/z (rel. intensity) 951 ([M-OCH₂CHCHPh]⁺, 9), 887 (9), 577 (8),477 (50), 118 (100).

Deprotection of AE^(F)-protected cinnamyl alcohol: A solution of 71 mg(0.065 mmol) of AE^(F)-OCH₂CH═CH-Ph and 1 mg (5 mol %) of CSA in 1 mL ofMeOH and 1 mL of Et₂O was stirred at room temperature for 1 h. Thereaction mixture was then transferred to a separatory funnel, andsaturated NaHCO₃ solution and FC-72 were added. The organic and aqueouslayers were washed with FC-72 (3×). The combined FC-72 extracts weredried (Na₂SO₄), and concentrated to give 60 mg (100%) of 22. The organiclayer was dried (Na₂SO₄), and concentrated to give 8.6 mg (98%) ofcinnamyl alcohol.

Preparation of 34b: A solution of dichlorodiphenylsilane (0.7 mmol),alcohol 22 (0.7 mmol) and triethylamine (0.77 mmol) in a mixture ofCH₂Cl₂ (2.5 mL) and benzotrifluoride (BTF, 2.5 mL) was heated at refluxfor 1.5 d. Solvents were evaporated and the residue was partitionedbetween FC-72 and CH₂Cl₂. The FC-72 phases were combined and evaporated.The residue was dissolved in CH₂Cl₂ (5 mL). Cyclohexanol (0.47 mmol),triethylamine (0.65 mmol) and dimethylaminopyridine (DMAP, 0.02 mmol)were added and the mixture was stirred at room temperature overnight.3-Phase extraction (NaHCO₃ solution, CH₂Cl₂, FC-72) yielded afterpooling and evaporation of the FC-72 phase a colorless oil. Filtrationover fluorous reverse phase silica (hexane/acetone 50:1) gave 0.24 g(47%) of 34b as a colorless oil which solidified upon standing: ¹H NMR(CDCl₃)δ 7.62-7.59 (m, 4H), 7.45-7.35 (m, 6H), 3.98-3.92 (m, 1H),3.82-3.73 (m, 1H), 2.3-1.9 (m, 4H), 1.9-1.6 (m, 8H), 1.5-1.3 (m, 3H),1.2-1.0 (m, 1H); ¹³C NMR (CDCl₃)δ 134.9, 132.8, 130.5, 128.0, 125-105(m, 16C), 71.8, 70.6, 35.5, 27.4, 27.2 (b), 25.4, 23.9; MS(EI) m/z (rel.intensity) 1204 (M⁺, 4), 1185 (5), 1126 (85).

Preparation of 37a: A solution of TBDPS-CL (26.5 mmol), alcohol 35 (24.1mmol), DMAP (1.2 mmol) and imidazole (33.8 mmol) in CH₂Cl₂ (50 mL) wasstirred at room temperature overnight. CH₂Cl₂ was added and the solutionwas washed with H₂O, 1 M HCl and brine. Drying (Na₂SO₄) and evaporationof the solvent yielded the TBDPS ether as a colorless oil: 15.5 g (92%)¹H NMR (CDCl₃)δ 7.69-7.66 (m, 4 H), 7.45-7.38 (m, 6H), 3.96 (t, 2H),2.45-2.25 (m, 2H), 1.07 (s, 9H); ¹³C NMR (CDCl₃)δ 135.2, 134.9, 129.9,127.9, 125-105 (m, 8C), 56.3, 33.9 (b), 26.6, 19.1.

Bromine (26.5 mmol) was added dropwise to a solution of the TBDPS et her(22.1 mmol) in 1,2-dichloroethane (150 mL) at 0° C. Stirring continuedat room temperature overnight. Distillation (0.03 mbar/105-110° C.)yielded 11.3 g (72%) of 36 as a colorless oil: ¹H NMR (CDCl₃)δ 7.69-7.65(m, 2 H), 7.48-7.39 (m, 3H), 4.11-4.06 (m, 2H), 2.47-2.35 (m, 2H), 1.01(s, 9H); ¹³C NMR (CDCl₃)δ 135.6, 134.9, 131.1, 128.1, 125-105 (m, 8C),57.0, 34.0 (b), 25.1, 21.4.

36 (1.1 mmol) was dissolved in CH₂Cl₂ (5 mL). Cyclohexanol (1 mmol),triethylamine (1.4 mmol) and dimethylaminopyridine (DMAP, 0.05 mmol)were added and the mixture was stirred at room temperature overnight.CH₂Cl₂ was added and the mixture was washed with NaHCO₃ solution. Theorganic phase was dried (Na₂SO₄), the solvent was removed and theresidue filtered through SiO₂ (hexane/EtOAc 98:2) to give 0.70 g (97%)of 37a as a colorless oil: ¹H NMR (CDCl₃)δ 7.65-7.60 (m, 2H), 7.42-7.35(m, 3H), 4.11 (t, 2H, J=6.9 Hz), 3.95-3.88 (m, 1H), 2.50-2.35 (m, 2H),1.84-1.72 (m, 4H), 1.52-1.40 (m, 3H), 1.30-1.21 (m, 3H), 0.94 (s, 9H);¹³C NMR (CDCl₃)δ 135.5, 132.3, 129.9, 127.8, 125-105 (m, 8C), 71.1,55.7, 35.7, 34.1 (b), 26.1, 25.6, 23.7, 18.8; HR-MS(EI) m/z found723.1597, calcd 723.1587.

Reactions and quenching were performed on a HP 7868 solution phasesynthesizer. Analysis of quenched samples was done with a HP 1100 seriesLC/MS. Samples eluted were compared with unreacted control samples.(R_(t) [min]: 2.6 (34a), 2.9 (34b), 2.3 (37a); Novapak C₁₈, 3.9×150 mm,1.2 mL/min, MeOH as eluent).

Protection of alcohols 38a-f. Alcohols 38a-f (0.16 mmol) were added to asolution containing the appropriate amount of reagents in 0.7 mL ofCH₂Cl₂. The samples were vortexed and left for 16 h. The solutions werewashed with H₂O, the organic phase was evaporated and the residue waseluted with hexane through cartridges containing SiO₂.

Deprotection of ethers 37a-f. Silyl ethers 37a-f were added to asolution of TBAF (0.6 M) in 0.5 mL of THF. After 3 h, Et₂O was added,the solutions were washed with H₂O (3 times), the Et₂O phase wascollected, evaporated and the residue was partitioned between FC-72 andCH₃CN. The organic phase was eluted with hexane/AcOEt through a SiO₂cartridge.

Although the present invention has been described in detail inconnection with the above examples, it is to be understood that suchdetail is solely for that purpose and that variations can be made bythose skilled in the art without departing from the spirit of theinvention except as it may be limited by the following claims.

What is claimed is:
 1. A compound having the formula:

wherein Rf¹ and Rf² are independently, the same or different, afluorohydrocarbon group, a perfluorocarbon group, a fluorinated ethergroup or a fluorinated amine group, Rs¹ is a spacer group selected froman alkylene group, a divalent phenyl group or an alkoxy alkylene group,d is 1 or 0, Rs² is a spacer group selected from an alkylene group, adivalent phenyl group or an alkoxy alkylene group, a is 1 or 0, R⁴ is analkyl group or an aryl group, R⁵ is an alkyl group or an aryl group, R⁶is H, an alkyl group, or a fluorinated alkyl group, and X is Cl, Br orI.
 2. The compound of claim 1 wherein Rf¹ and Rf² are independentlyperfluoroalkyl groups.
 3. The compound of claim 2 wherein theperfluoroalkyl groups have the formula —C_(n)F_(2n+1) wherein n is aninteger in the range of 4 to
 32. 4. The compound of claim 1 wherein atleast one of Rf¹ and Rf² is a perfluoroadamantyl group.
 5. The compoundof claim 1 wherein R⁵ is H.
 6. A compound having the formula:

wherein Rf¹ is a fluorohydrocarbon group, a perfluorocarbon group, afluorinated ether group or a fluorinated amine group, Rs¹ is a spacergroup is a spacer group selected from an alkylene group, a divalentphenyl group or an alkoxy alkylene group, d is 1 or 0, R⁴ is an alkylgroup or an aryl group, R⁵ is an alkyl group or an aryl group, and X isCl, Br or I.
 7. The compound of claim 6 wherein Rf¹ is a perfluoroalkylgroup.
 8. The compound of claim 7 wherein Rf¹ is —C_(n)F_(2n+1) whereinn is an integer in the range of 4 to
 32. 9. The compound of claim 6wherein Rf¹ is a perfluoroadamantyl group.